Pitch-impregnated fiber pipe

ABSTRACT

Disclosed is a pitch-impregnated fiber pipe having a surface coating of pitch containing aluminum pigment. The method of manufacture comprises suspending unimpregnated, conventionally manufactured porous fiber pipe tubes in a suspension of aluminum powder in the liquid pitch and forcing the pitch into the pores and interstices of the fiber pipe tubes.

United States Patent 191 Gannon Dec. 23, 1975 1 PITCH-IMPREGNATED FIBERPIPE [75] Inventor: Charles R. Gannon, Ashland, Ky.

[73] Assignee: Ashland Oil, Inc., Ashland, Ky.

[22] Filed: June 26, 1973 [21] Appl. No.: 373,626

Related US. Application Data [60] Division of Ser. No. 277,290, Aug. 2,1972, which is a continuation-in-part of Ser. No. 224,216, Feb. 7, 1972,abandoned.

2,384,671 9/1945 Fratis 117/168 X 2,768,119 10/1956 Nash 2,839,0886/1958 Biklen 138/146 X 2,886,459 5/1959 Lajoie 106/281 N X 3,039,4956/1962 Drukker.. 138/145 3,296,165 1/1967 Kemp .1 117/160 R 3,470,0069/1969 Brunel 106/123 FOREIGN PATENTS OR APPLICATIONS 276,584 3/1964Australia Primary Examine'rWil1iam D. Martin Assistant ExaminerStuart D.Frenkel [57] ABSTRACT Disclosed is a pitch-impregnated fiber pipe havinga surface coating of pitch containing aluminumpigment. The method ofmanufacture comprises suspending unimpregnated, conventionallymanufactured porous fiber pipe tubes in a suspension of aluminum powderin the liquid pitch and forcing the pitch into the pores andinterstices'of the fiber pipe tubes.

3,-C1aims, No Drawings PITCH-IMPREGNATED FIBER PIPE CROSS REFERENCE TORELATED APPLICATIONS This is a division of application Ser. No. 277,290filed Aug.2., 1972, which is a continuation-in-part of US. applicationSer. No. 224,216 filed Feb. 7, 1972, now abandoned, but copending at thedate of filing the Ser. No. 277,290 application.

FIELD OF INVENTION This invention relates to: porous articles improvedfor certain purposes by being at least partially saturated withimpregnants; to a process for making such impregnated articles; and toimpregnant compositions. The invention is concerned in one specificembodiment with pitch-impregnated fiber pipe, a method for manufacturingthe same, and pitch-impregnant compositrons.

PRIOR ART Porous articles are improved for certain purposes bysaturating them with an impregnant material, such as pitch. The desiredimproved properties obtained include increases in density, strength,durability, electrical resistance, insulating value, and resistance towater as well as decreased permeability and improved finish.

Impregnants (impregnating materials), satisfactory for industrial use,have been formulated with pitches derived from water gas tar, oil gastar, petroleum tars and sludges, and wood tar. The primary sources ofpitch impregnants are coal tar pitch derived from the pyrolysis of coaland pitch derived from petroleum. These have been used by themselves, inblends, or in combination with resins, oils, waxes, and other modifyingadditives. Such impregnants are widely used in the manufacture ofroofings, water-proofing compounds, insulating papers and fabrics,building boards, electrical insulators and conduits, felts and belts,brake linings, ceramic bodies and bricks. Coal tar pitch and pitchderived from petroleum have found a particularly important use in themanufacture of bituminized fiber pipe for use in sewer and drainagelines and as conduit for power and telephone cables.

The manufacture of bituminous-impregnated fiber pipe is well known inthe prior art. Ordinarily a pulp slurry of a fibrous material first ismade. Newsprint is a common material for the pulp slurry, although othermaterials such as chemical pulp and asbestos fibers may also be added. Awet web of interfelted cellulose fiber is deposited from the slurry ontoa felt roll. Subsequently the web is wound onto a mandrel to form a tubeof a desired wall thickness. Each wet tube on a supporting mandrel isthen passed through a drying oven, and the mandrel subsequently isremoved. The result is a dry paper tube of a desired wall thickness.There are a number of methods of impregnating the dry paper tubes with awater-proofing impregnant, which ordinarily is molten pitch. Thesemethods include simple soaking of the paper tubes in the impregnant,pressure saturation, vacuum saturation or a combination of pressure andvacuum saturation.

In the combination method a number of the dry paper tubes are firstplaced in a pressure vessel and subjected to a vacuum for severalminutes. The vessel, still at reduced pressure, is then filled withmolten pitch until the paper tubes are submerged. The molten pitch iscirculated for a period of time and the pressure in the vessel is thenrestored to atmospheric pressure thereby causing the molten pitch topermeate the pore spaces and interstices of the paper tubes. Theremaining molten pitch is drained from the pressure vessel and theimpregnated tubes are removed and quenched.

The pitch-impregnated tubes thus made are then ready for trimming of theends, machining and packaging for shipment. The pitch-impregnated fiberpipe thus manufactured is well suited for use as sewer pipe, undergroundconduit pipe for utility lines such as telephone cables and electricpower lines, and other uses where conditions of low pressures and highmoisture may be encountered. The pitch present in the pipe binds thecellulose fibers and imparts strength to the pipe as well as renderingit highly resistant to moisture. The fiber pipe is, however, notcompletely immune to the penetration of moisture. Under prolongedexposure to moisture, the pipe may eventually lose much of its originalstrength. A pitch-impregnated fiber pipe having increased moistureresistance thus is obviously desirable.

Pitch-impregnated fiber pipe is often stock-piled in open storage areaswhere it is exposed to temperature extremes, as well as to sunlight,rain, and snow. Consequently, over a period of time, the initiallyglossy black surface of the pipe deteriorates to a dull matte surface.Deterioration is thought to result primarily from exposure to theultraviolet fraction of sunlight. A fiber pipe possessing improvedresistance to exposure thus is highly desirable.

In the manufacture of fiber pipe coal tar pitch, as distinguished frompetroleum pitch, has been preferred in the past. Coal tar pitch enablesthe manufacture of a fiber pipe having suitable moisture resistance andresistance to weathering. This is primarily caused by the carbonparticles (quinoline insolubles) in coal tar pitch which filter to theinside and outside surfaces of the pipe during the impregnation process,thus forming a protective coating which renders the pipe moistureresistant and enhances its weather-resistant characteristics. Petroleumpitch has been available more recently and has found use as animpregnant either in blends with coal tar pitch or by itself.

Fiber pipe produced with a percent petroleum pitch impregnant, whichcontains very little suspended carbon particles, has, however, beenfound to be less resistant to moisture and to weathering than fiber pipecompletely impregnated with coal tar pitch or blends of petroleum pitchand coal tar pitch. Petroleum pitch thus has not been completelyaccepted as a sole impregnant for fiber pipe.

Although fiber pipe produced with coal tar pitch, or blends of coal tarpitch and petroleum pitch, exhibits excellent characteristics ofquality, persons exposed to the vapors during the impregnating processor to the coal tar pitch itself in the subsequent handling of the pipe,often experience skin irritation caused by the components of the coaltar pitch. In contrast, persons working with petroleum pitch by itselfhave not experienced this problem, thus making the use of petroleumpitch more desirable, particularly where ecological concern is of theutmost importance.

Another desirable property of pitch-impregnated fiber pipe would be asurface color other than the black color imparted by the pitch. Creatinga colored effect with sprayed coatings has been attempted in the past,but with little success. The solubility of pitch in the 3 paint vehiclehas always created unattractive blotching on the pipe surface.

Finally, a less publicized, but desirable surface property ofpitch-impregnated pipe, particularly on the interior surface, is reducedcoefficient of friction. Reduced friction requires less effort to pullbundles of cable through the pipe conduit.

An object of this invention; therefore, is to make a porous articlewhich is at least partially impregnated with an impregnant and has asurface film of impregnant containing at least partially dispersedaluminum pigment therein. Another object of this invention is to providea method of making such an article. Another object of this invention isto make a pitch-impregnated fiber pipe having improved resistance toattack by moisture and to weathering. Another object of this inventionis to enable the increased use of petroleum pitch either alone or incombination with other pitches as an impregnant for fiber pipe. Anotherobject of this invention is to provide a method of making apitchimpregnated fiber pipe having a uniform metallic surface. Stillanother object of this invention is to make available apitch-impregnated fiber pipe having uniform metallic interior andexterior surfaces which offer reduced friction resistance.

SUMMARY OF THE INVENTION In essence, this invention comprises: theprocess of impregnating porous articles with an impregnant containingsuspended aluminum particles; the article so impregnated having asurface-coating of impregnant containing suspended aluminum; and theimpregnant material itself. In one specific embodiment of the invention,bituminous impregnated fiber pipe is prepared by impregnating poroustubular forms with pitch containing suspended particulated aluminumtherein. In a still more specific embodiment, the fiber pipe isimpregnated with an unoxidized petroleum pitch containing a suspendedleafing aluminum pigment.

DETAILED DESCRIPTION OF THE INVENTION Generally speaking the article tobe impregnated, such as a building board, brick, ceramic body, roofingfelt, or fiber tube, must be sufficiently permeable to enablepenetration of the impregnant when the latter is applied to the surface.The article further must be stable at the temperature of impregnation.

The impregnant (the impregnating material) should have a low viscosityat the impregnating temperature to enable sufficient penetration intothe article being treated. The impregnant material must, however, bereasonably hard at ambient service temperatures. In addition, it isdesirable that the impregnant be low in filterable suspended matter(carbonaceous solids, dirt and mineral ash) particularly since aluminumparticles are to be added. If too much filterable suspended material isincluded, unsightly surface deposits on the finished article can resultor impregnation can be incomplete. The quantity of suspended matter thatcan be tolerated in the impregnant material will depend upon the articleto be treated (its nature, porosity, and wall thickness), the particlesize of the suspended material, viscosity of the impregnant fluid, andthe method of impregnation. Test methods of determining filterablespresent in impregnant materials are known in the prior art. Otherproperties desirable in the impregnating material, particularly if hightemperatures and vacuums are used, are limits on the content of lowboiling vo1a- Table I ASTM Designation 962 66 Maximum Amount Retained ona No. 325 (44 p.) Sieve Type Class A. B. C. Fine Medium Coarse 1.Leafing aluminum pigment powder 0.1% 1.5% 20% 2. Leafing aluminumpigment paste 0.1% 1.0% 15% 3. Non-leafing aluminum pigment powder 1.5%6.0% 20% 4. Non-leafing aluminum pigment paste 0.1% 1.0% 11.0%

The amount of aluminum pigment (powder or paste) added to the impregnantis determined by a number of factors. Aluminum pigments are expensive.Accordingly, the amount added should only be that necessary to provide aproper coating on the article being treated. The minimum amount will bethat necessary to achieve a desired improvement in the properties of thearticle.

As to the manner of impregnating an article with impregnant containingsuspended aluminum, any of the methods presently used in the art can beemployed. These include simple soaking in an open tank over a period oftime, pressure saturation, vacuum saturation, and combined pressure andvacuum saturation. This last method is a preferred method and is morefully discussed in a following portion of the description.

As noted previously, a more specific embodiment of this invention is themanufacture of bituminous impregnated fiber pipe in which fibrous tubesare impregnated with a pitch impregnant containing suspended aluminumpigment therein. In this particular embodiment the fibrous tubes to beimpregnated are of the kind presently used in conventional fiber pipemanufacturing. As discussed previously, they are made by winding a wetweb of cellulose pulp on a mandrel to the desired wall thickness andthen drying the tube either before or after it had been removed from themandrel. The technique of forming these dried paper tubes is well knownin the art and is discussed briefly in US. Pat. Nos. 1,803,409;1,854,230; and 1,860,674.

The pitches commercially available for manufacturing bituminous fiberpipe include coal tar pitch and petroleum pitch. Petroleum pitch, atleast for the purposes of describing this invention, may be eitheroxidized petroleum pitch or unoxidized petroleum pitch. Oxidizedpetroleum pitch is familiar to those skilled in the art, and is derivedby air blowing certain petroleum refinery flow streams to obtain adesired pitch product.

Unoxidized petroleum pitch can be further characterized as unmodifiedthermal petroleum pitch. These pitches remain rigid at temperaturesclosely approaching their melting points. The preferred procedure forpreparing the unoxidized petroleum pitch uses as starting material, aclarified slurry oil or cycle oil from which substantially all paraffinshave been removed in fluid catalytic cracking. Where the fluid catalyticcracking is not sufficiently severe to remove substanto the fact thatcertain metallic pigments occur in the form of thin flakes. When suchpigments are mixed with a vehicle and applied as a paint film, the thinflakes float and concentrate at the surface of the paint tially allparaffins from the slurry oil or cycle oil, they film where they overlapeach other. Aluminum powder may be extracted with furfural. In eithercase, the resulis treated with a leafing agent such as stearic acid totant starting material is a highly aromatic oil boiling at render itleafing, as well as to reduce the hazard of about 700 to 850F. This oilis thermally cracked at explosion. Leafing aluminum pigment can beprepared elevated temperatures and pressures for a time suffiby grindingaluminum in a ball mill in the presence of cient to produce a thermallycracked petroleum pitch mineral spirits or similar solvents. The mixtureis then with a softening point of about 150F to about 210F'. filtered toyield an aluminum paste. A typical leafing The manufacture of unoxidizedpetroleum pitches is aluminum pigment available commercially in pastedescribed in U.S. Pat. Nos. 2,768,119 and 3,140,248. form has thecompositions shown in Table III. Table 11 presents comparative proerties of four unoxidized petroleum pitches (A, B, C and D) and an oxi-15 TABLE III dzed (El 2 325511111153.1532 mesh 13183311315311? 7 TABLEII Test Test Method Pitch A Pitch B Pitch C Pitch D Pitch E SofteningPoint, F., R&B ASTM D-2398. 173 174 168.5 166 174 Density, G/cc Mettler1.192 1.205 1.160 1.178 1.186 Mod. Con. Carbon Wt.% ASTM D-2416 37.843.8 39.6 36.9 37.1 Flash, COC, "F. ASTM D-92 540 495 545 535 480 Pen.100/5/77 ASTM D-5 0 0 0 0 0 Pen. 200/60/115 ASTM D-5 128 47' 208 123Pen. 50/60/15 ASTM D-5 40 37 68 48 Sulfur, Wt.% ASTM D-l552 2.73 1.472.01 0.95 1.69 Benzene lns., Wt.% ASTM D-2317 0.80 11.7 1.9 2.3 8.1Quinoline lnsol., Wt.% ASTM D-2318 0.11 1 Nil Nil Nil Viscosity, CPS 350Brookfield 40 7O 45 32 70 (No.2 Spindle, 325 Brookfield 60 110 82.5 65125 RPM) 300 Brookfield 140 230 165 135' 240 (1) Quantity of solidscontent too great to pennit filtering At the time of filing the parentapplication, Ser. No. g fi 2?" 224,216, it was thought that a leafingaluminum in fl fig vjfj 0080 combination with an unoxidized petroleumpitch was Weight per Solid lallon 12.45 lbs. necessary to obtain thedesired improyernent in resis zfif g g 'zf g 85% tance to water and inweathering. This limitation ap- 44-150 microns 7% pears necessary onlyif it is desired to produce a fiber pipe product having smooth,metallic-colored or aluminized exterior and interior surfaces. Thus, anyalumi- It has been determined that some non-leafing aluminum pigment,particularly any of those described in num powders, when combined withan unoxidized pe- Table I, can be used in combination with coal tarpitch, troleum pitch, will also yield a metallic-colored oraluunoxidized (thermal) petroleum pitch, oxidized petrominized pipe. Itis believed that in these cases the stabileum pitch or mixtures ofthese. lizing agent added to the aluminum pigment to render The amountof aluminum powder or paste pigment it non-leafing is in fact decomposedwhen the alumiadded to the pitch impregnant will, of course, vary. Thenum pigment is heated to the temperature of the molminimum amount willbe that required to achieve a ten petroleum pitch, and that subsequentlythe alumidesired level of resistance in the finished product to numpigment acts as a leafing aluminum. Thus, almoisture or weathering. Themaximum amount will be though leafing aluminum powders are preferred inthe determined by the economics of the process and the specificapplication of the invention to manufacture the possibility of unevenpenetration of pitch if too much metallic-colored'or aluminized pipe,non-leafing alumifilterable aluminum pigment is suspended in the pitchnum powders,which will function as leafing pigments impregnant. Rangesof 0.1 to 1.4 percent or preferably at the temperature of impregnation,can also be used. 0.3 to 0.7 percent of aluminum pigment in a mixture ofReturning now to the broader concept of making a pitch and aluminum canbe used. These values for the pitch-impregnated fiber pipe using any ofthe commeraluminum concentration are based on aluminum alone cialaluminum pigments available as well as any of the and do not include anyadditional solvents or stabilizing common pitches available, these twomaterials can be materials which may be present. The ranges given arecombined in several ways to make the impregnating not restrictive. Lessor greater concentrations of alumimaterial. If the aluminum pigment hasbeen supplied in numcan be added. I paste form with a liquid carrier,the paste can be manulf pitch-impregnated pipe is to be manufactured havally added to the mass of molten pitch and the mixture ing, in additionto improved moisture and weathering agitated by stirring or circulation.For impregnating resistance, metallic or aluminized exterior andinterior purposes, the temperature of the aluminum powdersurfaces, thebest results are obtained if a leafing-type pitch mixture can be in therange of 275 to 37 5F. This aluminum pigment is used in combination withan untemperature will, of course, vary depending upon the oxidized(thermal) petroleum pitch. The term leafing is well known to those inthe art and is defined in Federal Test Method Standard No. 141. Leafingrefers properties of the particular pitch.

The step of impregnating the dry paper tubes can be performed in anymanner which will force the pitch into the pores and interstices of thepaper tubes. A preferred method is one wherein the paper tubes areplaced in a pressure vessel and subjected to a vacuum for a number ofminutes. The molten aluminum powder-pitch mixture is then pumped intothe pressure vessel until the tubes are submerged. The molten mixture iscirculated for a period of minutes to insure an even distribution ofpitch and aluminum. The pressure 0.68 percent in the final impregnantcomposition. The outside diameter of the pipe was 4 7/16 inches and thewall thickness was A inch. Samples of each specimen were then tested. Inthe copending parent application, data from tests having less relevancewas included in the test results reported. Only the data from thosetests deemed most relevant are included in this specification and are asfollows:

99.32% Petroleum Coal Tar Pitch Pitch (U0) ASTM 231 l 85% PetroleumPitch (U0) 0.68% Aluminum Specification Creep (23 hr.) .100 inch avg..084 inch Water absorption 1.04% average .75 8L .60% 2% Max. DryCrushing Strength, lb./ft. 800 average 920 800 Flatening .80% average.69 & .65% 3% Max.

" lnches of creep per two-inch section of pipe under 1000 psi at 68F,after 23 hours.

Percentage weight gain of original weight after 48 hours submersion inwater at 70F and atmospheric pressure. Load at rupture point in poundsper linear foot.

Percent reduction in diameter under 80 lbs/linear foot at 120F.

in the vessel is then raised to atmospheric pressure thereby forcing thepitch into the pore spaces of the paper tubes. The remaining moltenpitch-aluminum From the preceding table it will be noted that allproperties of the aluminized pipe were improved over those of pipeprepared with a conventional impregnatpowder mixture is then drainedfrom the vessel, and the 25 ing pitch.

Additional samples of fiber pipe impregnated with petroleum pitch (pitchsample D, Table 11) containing various concentrations of suspendedaluminum powder were prepared and tested. The pipe diameter again was 47/16 inches o.d. and the wall thickness inch. Re-

sults were as follows:

Pipe Dry lmpregnant Water Crushing Sample Composition Creep AbsorptionStrength Flattening A 0% Aluminum 100% Petroleum Pitch m 0.72 avg1.61-1.94 800 1.81-3.87 B .17% A1. 0.70 avg 1.48-1.83 840-800 1.96-2.10C .34% A1. 0.68 avg 1.58-1.57 720 2.04-2.18 D 68% A1. 0.72 avg 1.17-1.26760-700 1.06-1- E 1.36% Al. 0.51 avg. 0.63-0.60 920-1000 0.96-1.31

" Inches of creep per two-inch section of pipe under 1000 psi at 68F,after one hour.

Percentage weight gain of original weight after 48 hours submersion inwater at 70F and atmospheric pressure. Load at rupture point in poundsper linear foot.

Percent reduction in diameter under 80 lbs./linear foot load at 120F.

Unoxidized (thermal) petroleum pitch in all tests.

"' Percent of aluminum in total mixture.

"" This anomaly is attributed to experimental error.

and aluminum powder, other than leafing aluminum powder, are used, thepresence of aluminum powder in 50 the film of impregnant on the surfaceof the pipe is less readily apparent and may be completely masked.Usually visual examination of the pipe surface, however, shows ametallic glint in the black surface. If unoxidized petroleum pitch andleafing aluminum have been used, the aluminum particles because of theirleafing action tend to stay on the film surface yielding a pipe with ametallic aluminized surface.

The improved properties of aluminum powder-pitch impregnated fiber pipemade by this improved process have been demonstrated. In one test, aspecimen of pipe was prepared using a standard commercial impregnantcomprising 15 percent coal tar pitch and 85 percent unoxidized petroleumpitch. A second specimen was prepared using unoxidized petroleum pitchcorresponding to sample D from Table 11 mixed with powdered aluminumhaving the properties shown in Table III. The concentration of aluminumpowder was Sections of pipe samples A, B and C were tested in aconventional weatherometer for 619 hours, (the equivalent of 18 monthsoutdoor exposure). Results were as follows:

lmpregnant Observation 0% aluminum Petroleum Pitch Surface was dull,dusty brown.

.17% Aluminum Some evidence of aluminum-fiber surface still dull. .34%Aluminum Bright aluminum coating and film.

No dusting evident.

170F. Samples of each of these runs when tested yielded in the followingresults:

ing a porous tubular body impregnated with an impregnant consistingessentially of:

1% Aluminum 99% Petroleum 20% Coal Tar Pitch 100% Petroleum Pitch (U)ASTM D1861 80% Petroleum Pitch (U0) Pitch (UO) Range Avg. Standard WetCreep m .56 .38 .30-.46 .375 Water Absorpt on 1.13% 1.26% .781.02% 90%2% Max. Water Absorption 3.37% 3.85% 2.0-3.8% 2.82%

(200 hours) Dlgyltglrgshing Strength, 1140 1160 1100-1262 1165 m 1250Min.

. t. Flattening m 1.10 1.47 .78-l.62% 1.17% 3% Max.

" U0 indicates unoxidized petroleum pitch.

" Dry sample immersed in water and loaded at 1000 psi fiber stress for336 hours (two weeks). Percentage weight gain of original weight after48 hours submersion in water at 70F and atmospheric pressure. Percentageweight gain of original weight after 200 hours submersion in water at70F and atmospheric pressure.

Load at rupture point in pounds per linear foot. Percent reduction indiameter under 80 lbs/linear foot at 120F.

m Div-m1 um man: rut at: an! nnv r mm were at mnu'ra warm]. The "din-.24cnulmw rum 0 mm! n have "nun! M m mum! pa?" rum mun.

In another test a sample of pipe impregnated with an impregnantcomprising percent coal tar pitch, 1 percent aluminum and the remainderunoxidized petroleum pitch exhibited only 0.73 percent water absorptionafter submersion in water for five days. The average amount ofabsorption of a pipe sample impregnated only with 20 percent coal tarpitch and 80 percent pitch after five days would be about 1.5 percent.

Increased ease in handling aluminized pipe sections has been noted bypersons manually working with them. Aluminized pipe exposed to thesummer sun does not heat to as high a temperature as conventional blackpitch impregnated pipe. The aluminized pipe thus can be handled moreeasily with bare hands or thin gloves. Personnel have also noted thataluminized pipe sections are easier to load because the pipe lengthsmore readily slide over each other than do the conventional black pitchimpregnated pipe lengths.

Unless specifically indicated otherwise herein, all percentagecompositions listed herein are compositions by weight.

I claim:

1. An impregnated pipe having a uniform metallic exterior and interioraluminized surface and comprisa. unoxidized thermal petroleum pitch and,

b. leafing aluminum pigment of ASTM designation 926-66 in aconcentration of at least 0.3 percent by weight of both pigment andpitch, said unoxidized thermal petroleum pitch at least partiallypermeating into the pore spaces of said tubular body and forming a filmof pitch having a metallic aluminized surface of leafing aluminumpigment extending over the surface of said tubular body.

2. The pipe of claim 1 in which the porous tubular body comprisesinterfelted cellulose fibers.

3. An impregnated pipe having a uniform metallic exterior and interioraluminized surface comprising;

a. a porous tubular body of interfelted cellulose fibers;

b. solidified unoxidized thermal petroleum pitch at least partiallypermeating into the pore spaces of said tubular body, and forming a filmof pitch over the tubular body surface; and,

c. a metallic-appearing surface of leafing aluminum pigment of ASTMdesignation 962-66 on the exterior surface of said film of unoxidizedpetroleum pitch, the weight of aluminum pigment being at least 0.3percent by weight of the total weight of pitch and pigment.

1,. AN IMPREGNATED PIPE HAVING A UNIFORM METALLIC EXTERIOR AND INTERIORALUMINIZED SURFACE AND COMPRISING A POROUS TUBULAR BODY IMPREGNATEDWOITH AN IMPREGNANT CONSISTING ESSENTIALLY OF: A. UNOXIDIZED THERMALPETROLEUM PITCH AND, B. LEAFING ALUMINUM PIGMENT OF ASTM DESIGNATION926-66 IN A CONCENTRATION OF AT LEAST 0.3 PERCENT BY WEIEHGT OF BOTHPIGMENT AND OITCH, SAID UNOXIDIZED THERMAL PETROLEUM PITCH AT LASTPARTIALLY PERMEATING INTO THE PORE SPACES OF SAID TUBULAR BODY ANDFORMING A FILM OF PITCH HAVING A METALLIC ALUMINIZED SURFACE OF LEAFINGALUMINUM , PIGMENT EXTENDING OVER THE SURFACE OF SAID TUBULAR BODY. 2.The pipe of claim 1 in which the porous tubular body comprisesinterfelted cellulose fibers.
 3. An impregnated pipe having a uniformmetallic exterior and interior aluminized surface comprising; a. aporous tubular body of interfelted cellulose fibers; b. solidifiedunoxidized thermal petroleum pitch at least partially permeating intothe pore spaces of said tubular body, and forming a film of pitch overthe tubular body surface; and, c. a metallic-appearing surface ofleafing aluminum pigment of ASTM designation 962-66 on the exteriorsurface of said film of unoxidized petroleum pitch, the weight ofaluminum pigment being at least 0.3 percent by weight of the totalweight of pitch and pigment.